Welding electrode

ABSTRACT

The invention relates to a welding electrode for electric arc welding intended for joint welding and built-up welding stainless steels, particularly steels with a ferrite-martensitic, ferritemartensite-austenitic or martensite-austenitic structure, and is characterized in that the electrode in the shape of a bare wire or a wire with a coating deposits a weld metal whose alloying constituents affecting the structure lie within the following analysis limits: 0.01-0.05 percent carbon, 0.1-0.9 percent silicon, 0.5-4.5 percent manganese, 15.0-18.0 percent chromium, 4.5-7.5 percent nickel, 0.2-2.5 percent molybdenum, 0.02-0.12 percent nitrogen and 0.2-3.5 percent tungsten, the remainder iron apart from the unavoidable impurities. The alloying constituents shall be adapted manually in such a way that the following two equations with the chromium equivalent (Cre) and the nickel equivalent (Nie) are satisfied: Equation 1 Cre + Nie &gt; OR = 26.0 and &lt; OR = 32.0 Equation 2 1.4 X Cre - Nie &gt; OR = 15.0 and &lt; OR = 20.0 WHERE Cre % Cr + % Si + % Si + 0.5 X % W and Nie % Ni + 0.5 X % Mn + (% C + % N - 0.03 ); as a result the structure of the weld metal in a welded or heat treated condition contains martensite, ferrite, and austenite of such a composition that the martensite part lies between 5 and 50 percent and the ferrite plus austenite parts between 50 and 95 percent.

United States Patent Bjiirkroth I 1 WELDING ELECTRODE [72] Inventor:Jarl A. Blllrkmth, Avesta, Sweden [73] Assignee: Avelta JemverluAkflebolag,

Avesta, Sweden [22] Filed: June 24, 1971 [21] Appl. No.: 156,534

Related u.s. Application Data [63] Continuation of Ser. No. 786,472,Dec. 23,

1968, abandoned.

[52] US. Cl. ..219/137, 219/145, 29/504, 75/128 [51] Int. Cl. ..B23k9/00 [58] Field of Search ..75/128, 128 N, 128 W;

,1 9/ 1? 7 r. L i l [56] References Cited UNITED STATES PATENTS1,991,438 2/ 1938 Wohrman ..75/128 W 2,125,929 8/1938 Krivobok ..75/128W 2,150,901 3/1939 Amess ..75/128 N 2,214,128 9/1940 Fantana ..75/128 N2,229,065 l/ 1941 Franks ..75/128 N 2,405,660 8/1946 Norwood ..75/128 N2,848,323 8/1958 Harris ..75/128 N 3,215,814 11/1965 Dorshu ..75/128W3,489,551 l/ 1970 Fletcher ..75/128 W 3,123,469 3/1964 Tanczyn ..75/128W Oct. 24, 1972 [57] ABSTRACT The invention relates to a weldingelectrode for electric arc welding intended for joint welding andbuiltup welding stainless steels, particularly steels with aferrite-martensitic, ferrite-martensite-austenitic ormartensite-austenitic structure, and is characterized in that theelectrode in the shape of a bare wire or a wire with a coating depositsa weld metal whose alloying constituents affecting the structure liewithin the following analysis limits: 0.01-0.05 percent carbon, 0.1-0.9percent silicon, 0.5-4.5 percent manganese, 15.0-18.0 percent chromium,4.5-7.5 percent nickel, 0.2-2.5 percent molybdenum, 0.02-0.12 percentnitrogen and 02-35 percent tungsten, the remainder iron apart from theunavoidable impurities. The alloying constituents shall be adaptedmanually in such a way that the following two equations with thechromium equivalent (Cr,,) and the nickel equivalent (Ni are satisfied:

Equation 1 Cr, +Ni 26.0 and 32.0 Equation 2 1.4 X Cr Ni, 15.0 and whereCr Cr Si Si +0.5 X W and Ni,,=% Ni +0.5 X Mn C N 0.03 as a result thestructure of the weld metal in a welded or heat treated conditioncontains martensite, ferrite, and austenite of such a composition thatthe martensite part lies between 5 and 50 percent and the ferrite plusaustenite parts between 50 and 95 percent.

4 Claims, No Drawings WELDING ELECTRODE This application is acontinuation of application Ser. No. 786,472, filed Dec. 23, 1968, nowabandoned.

Certain types of stainless steels particularly steels with aferrite-martensitic, ferrite-martensite-austenitic ormartensite-austenitic structure, obtain high mechanical strengthcharacteristics, partly owing to their chemical composition and partlyby the heat treatment they undergo prior to being used. Austeniticstainless steels in a heat-treated condition, on the other hand, have alow yield limit, but they may be given a higher yield limit and ultimatestrength values by cold work, e.g., by stretching.

In welding stainless steels one aims at obtaining a weld metal with achemical composition and characteristics which correspond to those ofsteel both from a corrosion viewpoint and other viewpoints. If one weldsferrite-martensitic, ferrite-martensite-austenitic ormartensite-austenitic steels with electrodes having an analysisidentical to that of the steel the melted weld metal in an unannealedcondition will have a high yield limit and ultimate strength but, on theother hand, a very insignificant elongation and impact value. By asubsequent heat treatment the elongation and impact value of the weldmetal may be improved; however it has been very difficult to reach fullconformity to he properties of the steel. 3

As regards welding, the elongation value of the weld metal may beregarded as a gauge of the welds cracking resistance. When welding iscarried out with electrodes which deposit a weld metal with too lowelongation values the risk of contraction cracks in the weld is great.When welding ferrite-martensitic, ferritemartensite-austenitic ormartensite-austenitic steel with the corresponding electrodes one hastherefore normally applied a method which implies both the preheating ofthe basic material and the stress-relieving of the welded structure inorder to reduce the risk of cracks.

In addition to high strength certain new ferrite-martensite-austeniticsteel also possesses an improved weldability, which means thatpre-heating has to be applied very seldom. As an example one may mentionthat a steel with a low carbon content of the type 16 percent chromium,5 percent nickel and 1 percent molybdenum which after a double heattreatment obtains yield limit values over 80 kp/mm, an elongation ofabout percent and an impact value over 7 kpm/cm In welding this steelwith previously known electrodes it has not been possible to obtain aweld metal which in an unannealed condition possesses the correspondingvalues. On the other hand the characteristics of the weld metal could beimproved by a suitable heat treatment so that they on the wholecorrespond to those of the steel.

According to the present invention it is possible without subsequentheat treatment to obtain a weld metal with a high yield limit andultimate strength in combination with very good elongation and impactvalue by using an electrode which, in the shape of a wire or a wire witha coating deposits a weld metal which contains the following alloyingconstituents affecting the structure: 0.01-0.05 percent carbon, 0.1-0.9percent silicon, 0.5-4.5 percent manganese, 15.0-18.0 percent chromium,4.5-7.5 percent nickel,

0.2-2.5 percent molybdenum, 0.02-0.12 percent nitrogen and 0.2-3.5percent tungsten the remainder being iron apart from the unavoidableimpurities. The content of undesirable impurities, such as sulphur,phosphorus, copper, lead, etc., shall be as low as possible.

The alloying constituents affecting the structure shall be adaptedmutually in such a way that the following two equations with thechromium equivalent (Cr and 0 the nickel equivalent (Ni are satisfied:

Equation 1: Cr +Ni 26.0 and S 32.0

Equation 2: 1.4XCr "Ni 15.5 and 20.0 where Cr Cr+% Si Mo +0.5 W; andNi,,=% Ni+0.5 X% Mn+30 (%C+% N0.03).

A welding electrode which satisfies the pre-requisites indicated abovedeposits a weld metal with a structure composed of ferrite, martensiteand austenite. If these three structure elements are balanced againsteach other the weld metal, without subsequent heat treatment, obtainsyield limit values of about 60 kp/mm and ultimate strength values ofabout 82 kp/mm while at the same time as the elongation is about 30percent and the impact value over 10 kpm/cm at room temperature. Inaddition one obtains a lowered transition temperature, so that the weldmetal still at C possessies impact values over 6 kpm/cm and attemperatures about to C meets the impact value requirements which arenormally specified for vessels under pressure.

The addition of tungsten to austenitic stainless electrodes is knownalthough the effect achieved has not been described in greater detail.In the present invention tungsten acts as a kind of modulator which incombination with nickel, manganese and nitrogen gives the desiredbalance to the ratio between the martensite part and the ferrite plusaustenite parts. According to the present invention the martensite partof the weld structure shall lie between 5 and 50 percent and the ferriteplus austenite parts between 50 and 95 percent.

Consequently the present invention relates to an electrode or a fillerfor joint-welding or built-up welding stainless steels, particularlysteel with a ferrite-martensite-austenitic structure, e.g., steel oftype 16 Cr 5 Ni 1 Mo, as well as steel of a ferrite-martensitic ormartensite-austenitic structure, e.g., steel of type 12-14 Cr, 0-3 Niand 0-2 Mo. In the process of welding with electrodes according to thepresent invention the weld metal in itself does not require any heattreatment after the welding in order to achieve maximum toughness. Incertain cases, on the other hand, the basic material may requirestress-relieving in order to eliminate welding stresses or in order tolevel out the hardness tops which the latter types of steel show inheat-affected zones close to the weld. With the electrode described itis also possible to carry out stress-relieving within the temperaturerange 550-700C without causing the strength values of the weld materialto decrease to any great extent.

In addition the electrode is suitable for welding certain austeniticstainless steels, provided that the corrosion conditions to which thewelded object is subjected, suit the weld metal of the electrode. Theelectrode is particularly suitable suited for joint welding stainlesssteels of identical or almost identical composition containing at least13 percent chromium, and 3.5 percent nickel; they are then merged bymeans of arc welding and melting of a coated or an uncoated electrodewhose composition lies within the composition according to claim 1.

By hardfacing or deposit welding the electrode is also very suitable forcoating a surface on work-pieces of unalloyed, low-alloyed or stainlesssteels; the hardfacing then takes place with an electrode which, coatedor uncoated, has a composition according to that of claim 1.

The welding electrode according to the present invention may be made inthe shape of coated electrodes or uncoated wire for melting in an inertprotective gas atmosphere or under a protective blanket of granulatedwelding powder, so-called flux. The bare wire in its turn may behomogeneous or so-called pipe-wire.

The covering of coated manual-welding electrodes consists of fluxingmaterial, arc-stabilizing, deoxidizing and alloying elements as well assome plasticizer for making the substance ductile. The composition ofthe covering may be varied and may have a lime-basic, rutile-basic orrutile-acid character all according to the welding properties desired.It is essential for this embodiment within the scope of the inventionthat the covering should contain a certain amount of one or several ofthe following alloying elements: chromium, nickel, molybdenum, tungsten,manganese, silicon and nitrogen, partly in order to compensate the lossby burning which normally occurs in connection with the transport ofmaterial through the arc and partly in order to provide the weld withthat part of the alloying elements which possibly for practical reasonshas not been alloyed into the core wire.

According to the second embodiment, i.e., an uncoated filler wire formelting in an inert protective gas or under a protection blanket ofgranulated welding powder, the composition of the wire in the casementioned first shall conform as nearly as possible to the desired weldanalysis and in the latter case be adapted to the composition of thewelding powder.

Examples of some differently coated electrodes and their characteristicsare given below in Tables I and II:

Table I chemical analysis The chemical analysis has been made in themanner prescribed in different standards, e.g., DIN 8556, Blatt 2(Deutsche Industrie Normen), i.e., one makes a weld on plate with agreat number of beads and determines the chemical analysis of that partof the weld which is further than 10 mm from the plate. In doing so theeffect of the basic material is eliminated. Table II characteristics ofstrength The values indicated above represent an average of severaltests. The welding tests have been carried out with a coated electrodein the manner prescribed in DIN 1913, Blatt 2. For the all-weldedtensile tests, test specimens of type 10C50 according to SIS 1121 13(SIS The Swedish Standard Association) and for the impact tests CharpyV-notch specimen according to SIS 1123 51 have been used. The F2 testindicated above is heat-treated at 600C with subsequent aircooling.

Iclaim:

l. A method of arc welding high strength stainless steels comprising thesteps of melting an electrode in an electric are, said electrode havingthe following composition: 0.01-0.05 percent carbon, 0.l-0.9 percentsilicon, 0.5-4.5 percent manganese, 15.0-18.0 percent chromium, 4.5-7.5percent nickel, 0.2-2.5 percent molybdenum, 0.02-0. 12 percent nitrogen,02-35 percent tungsten, and the remainder essentially iron, theconstituents being adapted so that the chromium equivalent plus thenickel equivalent is not less than 26.0 and not more than 32.0, and 1.4times the chromium equivalent minus the nickel equivalent is not lessthan 15.0 and not more than 20.0, the chromium equivalent being the sumof the percent chromium percent molybdenum percent silicon 0.5 timespercent tungsten and the nickel equivalent being the sum of the percentnickel 0.5 times percent manganese 30 (percent carbon percent nitrogen0.03) so as to obtain a weld metal having a microstructure comprisingferrite, martensite, and austenite, the martensite comprising from 5percent to 50 percent thereof and the sum of the ferrite and austenitecomprising from 50 percent to percent thereof.

2. A method according to claim 1 wherein the electrode is bare wire andincluding the step of melting the electrode in an inert protective gasatmosphere.

3. A method according to claim 1 wherein the electrode is a bare wireand including the step of melting the electrode under a protectiveblanket of granulated welding flux.

4. A method according to claim 1 wherein the welding electrode is a wirehaving a coating comprising fluxing material, arc-stabilizing material,deoxidizing material, and at least one material selected from the groupof alloying elements consisting of chromium, nickel, molybdenum,tungsten, manganese, silicon and nitrogen.

Po-wso UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,7Q0,85l D t October 24, 1972 lnventofls) Jarl A. Bjorkroth It iscertified that'errorappears in the above-identified patent and that saidLetters Patent are hereby corrected as shown below:

ABSTRACT, line 15, "manually" should read ---mutually--; lines 19 and20, Equations 1 and 2, after "Ni insert and after "and" insert line 22,Si"

(first occurrence) should be Mo-; line 23, after "MN insert --30--.Column 1, line 28, "he" should read --the-. Column 2, lines ll and 12,Equations 1 and 2, after "Ni insert line 60, "material" should read-metal Column 4, lines 3 and 4, "Table v II characteristics of strength"should appear on a separate line, as a heading.

Signed and sealed this ZZndday of May 1973.

(SEAL) Attest:

EDWARD M .FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents *zgz g UNITED STATES PATENT OFFICE CERTIFICATE OF CQRRECTIONPatent N 3,700,851 D t d October 24, 1972 lnventofls) Jarl A. BjorkrothIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

ABSTRACT, line 15, manually" should read *--mutually--; lines 19 and 20,Equations 1 and 2, after "Ni insert --Z- and after "and" insert line22,."% Si" (first occurrence) should be Mo-; line 23, after "MN insert--30--. Column 1, line 28, "he" should read --the--. Column 2, lines 11and 12, Equations 1 and 2, after "Ni insert line 60, "material" shouldread --metal- Column 4, lines 3 and 4, "Table v II characteristics ofstrength" should appear on a separate line, as a heading.

Signed and sealed this ZZndday of May 1973.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD M.FLETCHER,JR.Attesting Officer

2. A method according to claim 1 wherein the electrode is bare wire andincluding the step of melting the electrode in an inert protective gasatmosphere.
 3. A method according to claim 1 wherein the electrode is abare wire and including the step of melting the electrode under aprotective blanket of granulated welding flux.
 4. A method according toclaim 1 wherein the welding electrode is a wire having a coatingcomprising fluxing material, arc-stabilizing material, deoxidizingmaterial, and at least one material selected from the group of alloyingelements consisting of chromium, nickel, molybdenum, tungsten,manganese, silicon and nitrogen.